Hi, thanks for the query to H.C.M.
that too the size of a golf ball and still not resolves so this is the cause of concern.
Two points are here,
1 IF any blunt injury
over bruised part in recent past. If yes, than please at once consult a surgeon and get in a MRI
of diseased part to rule out any pathology for type of tumor
2 If no injury than it might be due to some sting ( insect bite) so please be careful about these things.
Second reason is not cause of concern but first reason is very dangerous ( in few patients)
as you said diagnosed earlier , it is presuming that you had taken treatment of this much earlier so nothing is to worry.
Toenails color is blue or purple , this may be due to compression of blood supply rout to toenail by swelling , so important thing to be noted is to rule out any serious disease .
Good luck Dr. HET.